Supercritical water oxidation apparatus and process

ABSTRACT

A method for oxidizing an organic material includes the steps of (a) forming a preoxidation mixture comprising the organic material and water, and (b) causing the preoxidation mixture to react with a liquid oxidizer in a continuous flow reactor supercritical conditions for water, including a pressure of at least 3206 psia and a temperature of at least 705° F., to form a post-oxidation mixture containing condensible material and non-condensible material, wherein substantially all of the organic material has been oxidized.

FIELD OF THE INVENTION

This invention relates generally to processes and equipment forprocessing organic contaminants and, more specifically, to processes andequipment for destroying organic contaminants using supercritical wateroxidation methods.

BACKGROUND OF THE INVENTION

Supercritical water oxidation (SCWO) processes can be used to destroyliquid or slurry organic waste streams, especially low volume organicwaste streams. SCWO processes take advantage of the unique properties ofwater at conditions near and beyond the thermodynamic critical point ofwater (705° F. and 3206 psia). Above the critical point, water has thecharacteristics of a very dense gas. Organic materials and gases aremiscible in this dense water vapor. Thus, above the critical point,liquid or slurry organic waste streams can be readily oxidized anddestroyed with very high efficiency.

SCWO processes are well-known in the art. For example, U.S. Pat. Nos.2,944,396, 4,543,190, 5,387,398, 5,405,533, 5,501,799, 5,560,822,5,804,066, 6,054,057, 6,056,883, 6,238,568, 6,519,926, 6,576,185,6,709,602 and 6,773,581, the entireties of which are incorporated hereinby this reference, describe various forms of SCWO processes.

In a typical SCWO process, a feed stream containing water and an organicwaste material is pressurized, mixed with an oxidizer and caused toreact in a plug flow reactor. Thermal energy produced by the oxidationreactions provides the necessary preheat for the reactants. If the feedstreams have an inadequate heating value, supplemental fuel is added orthe feed streams are preheated. The reactor is designed to provide therequired residence time (typically less than about one minute) atsupercritical conditions.

Unfortunately, SCWO processes of the prior art are unduly expensive tooperate and maintain. For example, depending upon the feed stream, aconsumable reactor liner may be required to protect the interior reactorwalls from the highly corrosive combustion process and the resultingreaction products. Such a liner may need to be replaced as frequently asevery 60-70 hours of operation, resulting in considerable maintenanceand operating costs associated with the resulting down time. Othersignificant costs associated with prior art SCWO processes are thecapital costs and operating costs required in providing compressedoxygen or compressed air at 3500-4000 psig. Typically, the operatingcosts involved in operating air compressors for a SCWO reactor accountfor greater than 90% of the total operating cost.

Another cost associated with prior art SCWO processes is the largeamount of aqueous reaction products produced in the process. Typicallysuch aqueous reaction products present an expensive problem to theoperator of the process. Moreover, reaction product salts tend toprecipitate out in down stream equipment resulting in the fouling ofsuch equipment, requiring frequent and expensive maintenance to removesuch salts.

Accordingly, there is a need for a SCWO process which avoids orminimizes the aforementioned problems in the prior art.

SUMMARY

The invention satisfies this need. The invention is a method ofoxidizing an organic material comprising the steps of (a) forming apreoxidation mixture comprising the organic material and water, and (b)causing the preoxidation mixture to react with a liquid oxidizer in acontinuous flow reactor supercritical conditions for water, including apressure of at least 3206 psia and a temperature of at least 705° F., toform a post-oxidation mixture containing condensible material andnon-condensible material, wherein substantially all of the organicmaterial has been oxidized.

In one embodiment of the invention, the liquid oxidizer is hydrogenperoxide solution, typically a 50 weight percent hydrogen peroxidesolution.

In another aspect of the invention, the invention is a reactor useful inthe continuous oxidation of organic materials in an SCWO process. Thereactor comprises a reactor body with reactor walls and a threadedreactor upper plug. The reactor also comprises a cylindrical linerattached solely to the threaded reactor upper plug, such that, when thethreaded reactor upper plug is removed from the reactor, the reactorliner is consequently and simultaneously removed from the reactor aswell.

In yet another aspect of the invention, the invention is a reactoruseful in the continuous oxidation of organic materials in an SCWOprocess, wherein the reactor comprises an internal letdown valve. In atypical embodiment of this aspect of the invention, the internal letdownvalve comprises a heat shield, a needle seat and a piston actuatedneedle. In another embodiment of the internal letdown valve, the letdownvalve comprises a heat shield, a needle seat and a bellows operatedneedle. In either case, the vertical needle position is modulated by apressure feedback loop to control vessel pressure. During operation,there is sufficient clearance between the needle and the needle seat toallow salt precipitated in the vessel to be swept through the internalletdown valve for collection later in the process stream.

DRAWINGS

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription, appended claims and accompanying drawings where:

FIG. 1 is a flow diagram illustrating a SCWO process of the prior art;

FIG. 2 is a process flow diagram illustrating a SCWO process havingfeatures of the invention;

FIG. 3 is a perspective drawing, in partial cutaway, of a SCWO reactorhaving features of the invention;

FIG. 4 is a detailed perspective drawing, in partial cutaway, of theupper portion of the reactor illustrated in FIG. 3;

FIG. 5 is a perspective view of a threaded plug and liner portion of thereactor illustrated in FIG. 3;

FIG. 6 is a detailed perspective drawing, in partial cutaway, of thelower portion of the reactor illustrated in FIG. 3;

FIG. 7 is a cross-sectional side view of an integrated letdown valve andfunnel used in the reactor illustrated in FIG. 3;

FIG. 8 is a flow diagram illustrating an O-ring cooling system useful inthe invention; and

FIG. 9 is a diagram illustrating pressures exerted upon an internalletdown valve useful in the invention.

DETAILED DESCRIPTION

The following discussion describes in detail one embodiment of theinvention and several variations of that embodiment. This discussionshould not be construed, however, as limiting the invention to thoseparticular embodiments. Practitioners skilled in the art will recognizenumerous other embodiments as well.

The invention is a method of oxidizing an organic material comprisingthe steps of (a) forming a preoxidation mixture comprising the organicmaterial and water, and (b) causing the preoxidation mixture to reactwith a liquid oxidizer in a continuous flow reactor supercriticalconditions for water, including a pressure of at least 3206 psia and atemperature of at least 705° F., to form a post-oxidation mixturecontaining condensible material and non-condensible material, whereinsubstantially all of the organic material has been oxidized.

In the invention, the liquid oxidizer is typically hydrogen peroxide,most typically hydrogen peroxide in a 50 weight percent solution.

The invention differs from most SCWO oxidizing methods of the prior artwherein the oxidizer is either pure oxygen or air. Accordingly, theinvention as illustrated in the flow diagrams set forth in FIG. 2 iscontrasted with most prior art SCWO oxidizing methods using gaseousoxygen as illustrated in FIG. 1.

The use of a liquid oxidizer eliminates the need for a high pressurecompressed air system. This results in a substantial space and costsavings. Eliminating the high pressure compressed air system alsoeliminates the operating hazards associated with such a system. Insteadof having to use an air compressor with a massive 300 horsepower motor,hydrogen peroxide can be supplied to the reactor by a simple 7.5horsepower pump.

The invention can be practiced in the reactor 10 illustrated in FIG. 3.The reactor 10 comprises a cylindrical reactor body 12 which is cappedat the top by an upper plug 14 and is capped at the bottom by a valvehousing 16.

The reactor body 12 is typically made from corrosive resistant materialssuch as 316 stainless steel or high nickel stainless steels. Thethickness of the reactor body walls 18 is designed to safely contain thetemperatures and pressures present during operation.

Within the reactor body 12, between the upper plug 14 and the valvehousing 16, is defined an oxidation zone 20 wherein the oxidationreactions take place during operation. Typical operating conditionswithin the oxidation zone 20 include pressures of about 3500 psig andtemperatures of about 1200° F.

A protective liner 22 is disposed within the oxidation zone 20,proximate to the interior surfaces of the reactor body walls 18 toprotect the reactor body walls 18 from chemical degradation caused bycorrosive conditions generated during the oxidation process.

The liner 22 is typically made from a chemical resistant material, suchas nickel-molybdenum-chromium-tungsten alloy (such as Hastelloy™, UNS N10276), ceramics, or platinum. In a typical operation, when the liner ismade from a nickel-molybdenum-chromium-tungsten alloy, it is betweenabout 0.125 inches and about 0.750 inches in thickness.

The disposition of the liner 22 within the oxidation zone 20 defines anarrow annulus 24 between the walls 18 of the reactor body 12 and theliner 22. The annulus 24 is purged with a small but constant flow offlushing water to chemically protect the reactor body walls 18. The flowrate of flushing water is typically less than about 1 gallon per minute.

Cooling water jackets 26 a and 26 b, respectively, are providedsurrounding the upper end 28 of the reactor body 12 and around the lowerend 30 of the reactor body 12 to provide cooling to those areas of thereactor 10 during operation.

Cooling water piping 32 is provided about the exterior of the reactor 10to provide cooling water to strategically located injection ports 34along the reactor 10.

Induction heating coils 36 are disposed around the reactor 10 to provideheating to the oxidation zone 20 during operation. The induction heatingcoils 36 are used to bring the oxidation zone 20 to normal operatingconditions during startup and to add the energy necessary to maintainthe required oxidation zone 20 operating conditions when processing feedstreams which do not contain an adequate amount of energy to maintain aself-sufficient reaction. Accordingly, use of induction heating coils 36allows the destruction of low BTU value waste streams without requiringthe use of supplemental fuels.

The use of induction heating coils 36 thus permits process heat upwithout the necessity for large quantities of supplemental fuels andwithout the generation of large quantities of heat up liquid. Also, inprior art SCWO designs, the use of supplemental fuels necessarilyrequires considerable volumes of process water. Still further, in priorart SCWO designs, dilution water is used to transport salts as thereaction products exit the reactor 10. By contrast, no dilution water isrequired in the present invention. Salts exit the reactor 10 in anon-fouling gas solid suspension (since the steam is only condensedafter its exit from the reactor 10).

The upper plug 14 is illustrated in detail in FIGS. 4 and 5. The upperplug 14 is provided with exterior threads 38 which are sized anddimensioned to cooperate with interior threads 40 defined in the reactorbody walls 18 of the upper end 28 of the reactor body 12. Both sets ofthreads 38 and 40 are preferably ACME threads to positively seat sealrings 42.

The seal rings 42 are provided around the upper plug 14 to providesealing between the upper plug 14 and the reactor body 12. Cooling wateris injected between the seal rings 42 via injection nozzles 48.

Independent cooling systems, such as those illustrated in FIG. 8, arepreferably provided for each pair of seal rings 42. Each independentcooling system is comprised of a circulation pump 90, a heat exchanger92, a surge tank 94, a high level alarm 96 and a low level alarm 98.Should a seal ring 42 seal failure occur, the leakage past a primaryseal ring 42 will cause its surge tank 94 level to rise, therebyactivating its high-level alarm 96. In the event of a backup seal ring42 failure, the surge tank 94 level would drop due to coolant leakage,thereby activating the low-level alarm 98.

The use of a threaded upper plug 14 also provides for simplified upperplug fabrication. Prior art SCWO system designs require the use of aforged, flanged head, whereas, in the invention, the upper plug 14 canbe fabricated from readily available, high-quality pressure vesselmaterials. The threaded upper plug 14 eliminates the need for forgingprior to machining, and thus reduces fabrication time. The threadedupper plug 14 also reduces the time necessary to replace the liner 22.

As illustrated in FIG. 5, the liner 22 is attached to the upper plug 14by press fit retainer pins 50. Using this design, the upper plug 14 andthe liner 22 are a single, integral assembly. Accordingly, the removalduring maintenance of the upper plug 14 consequently and simultaneouslyremoves the liner 22 at the same time.

In one embodiment of this design, to separate the liner 22 from theupper plug 14, the press fit retainer pins 50 are driven inwardly, intoan annulus (not shown) within the upper plug 14. The annulus issufficiently large to allow the retainer pins 50 to be fully removedfrom the liner 22 and upper plug 14 by driving them further inward.

In another embodiment of this design, the press fit retainer pins 50 aremachined with heads on them which limit inward travel, therebyprecluding the possibility of the pins inadvertently loosening. In thisembodiment, the liner 22 is separated from the upper plug 14 by graspingthe heads on the press fit retainer pins 50 and pulling them outward.

Prior art SCWO designs utilizing a forged, flanged head retain theflanged head in place with torqued bolts to form the upper boundary ofthe oxidation zone 20. With the threaded upper plug 14 of the invention,no torquing is required. Thus, the threaded upper plug 14 of theinvention is much quicker and easier to install and remove.

Also, during routine liner 22 change outs, a spare threaded upper plug14 with a new liner 22 attached can be staged before removing the oldassembly. Removing the old assembly and installing the newly stagedassembly thus further reduces maintenance downtime.

In one embodiment of the invention, feed stream ports 54 a and 54 b areprovided at the top of the upper plug 14 for inputting hydrogen peroxideand for inputting a combined water and organic waste preoxidation feedstream mixture, respectively. Separate passageways are defined withinthe upper plug 14 to carry the preoxidation feed stream mixture and thehydrogen peroxide feed stream to the bottom portion of the upper plug14, whereupon both feed streams are injected into the oxidation zone 20.

The valve housing 16 is illustrated in detail in FIGS. 6 and 7. Thevalve housing 16 is threaded with exterior threads 58 which are sizedand dimensioned to cooperate with interior threads 60 disposed in thelower end 30 of the reactor body 12. Preferably, threads 58 and 60 areACME threads. Seal rings 62 are disposed around the valve housing 16 toprovide sealing between the valve housing 16 and the reactor body 12. Asis the case with the seal rings 42 disposed around the upper plug 14,each seal ring 62 pair preferably has its own independent coolingsystem. Each independent cooling system is comprised of a circulationpump, a heat exchanger, a surge tank, and a control cylinder end cup andlevel alarms. Typically, however, the lowest seal ring 62 pair is notcooled.

Disposed within the valve housing 16 is a heat shield 64 and a letdownvalve 66. The heat shield 64 is typically made from Hastelloy™ (UNS N10276), high nickel alloys or various ceramic compositions. The heatshield 64 is dimensioned to collect solids from the oxidation zone 20and to sweep the solids to a central aperture 67.

The letdown valve 66 comprises a valve seat insert 44, a ball cap 46, apressure control needle 68 and a floating control valve piston 72. Thevalve seat insert 44 is positioned directly below the heat shield 64.The valve seat insert 44 provides a seating surface for the controlneedle 68.

The valve seat insert 44 fits tightly into the ball cap 46. The ball cap46 maximizes the flow area for low pressure, high volume gases afterthey flow past the pressure control needle 68. The outer profiles of theball cap 46 and the heat shield 64 are designed to slip into the valvehousing 16 from the high pressure side and seat against a tapered seatin the valve housing 16.

The relationship between the pressure control needle 68 and the controlvalve piston 72 maintains the pressure control needle 68 centered andvertical.

The pressure control needle 68 is machined, typically from Hastelloy™(UNS N 10276), high nickel alloys or various ceramic compositions. Theunderside of the ball cap 46 is contoured to match the dimensions of thepressure control needle 68. The bottom of the pressure control needle 68fits into the top of the control valve piston 72 employing a machinetaper similar to a Morse taper and is firmly bolted in place.

The pressure control needle 68 preferably has one or more small slots 74machined into the seating surface to establish minimum flow through thevalve when the pressure control needle 68 is fully seated in the valveseat insert 44. In the embodiment illustrated in the drawings, the oneor more slots 74 is a single helical slot defining nearly horizontalgrooves 80 in the exterior of the pressure control needle 68.

Gases and precipitated solid salts from the reaction chamber are routedinto the letdown valve 66 by the heat shield 64. Salts which are formedby the combustion process within the oxidation zone 20 are carried withthe superheated steam through the letdown valve 66. The salt andsuperheated steam are directed to a reactor exit port 82. The pressurecontrol needle 68 serves as a movable throttling element in the letdownvalve 64 to control pressure within the oxidation zone 20. As thereaction products flow past the pressure control needle 68, the reactionproducts are flashed to relatively low pressure superheated steamcarrying the salts in suspension.

Pressure within the oxidation zone 20 is further controlled bypressurized control fluid provided through a control port 76 disposed atthe base of the valve housing 16. The control valve piston 72 typicallyhas between about ⅓ inch and about 1½ inch of axial float depending uponthe size and shape of the pressure control needle 68. The axial float isset up by the dimensional allowances of the valve seat insert 44, ballcap 46, pressure control needle 68 and control valve piston 72. Thecontrol valve piston 72 position is controlled from outside the reactor10 via the control port 76.

As salt deposits build up above the seating surface between the pressurecontrol needle 68 and the valve seat insert 44, pressure slowly rises inthe oxidation zone 20. This pressure rise causes a pressure feedbackloop (described below) to call for greater letdown valve 66 opening,resulting in the salt deposits being swept into the exit port 82 throughthe letdown valve 66.

In one embodiment of the invention, one or more generally horizontalgrooves 80 are machined around the upper exterior of the pressurecontrol needle 68. Such groove or grooves 80 can be discreet or suchgroove or grooves 80 can be continuous, such as the grooves 80 definedby the helical slot 74 illustrated in the drawings. During operation,when the grooves 80 are exposed to the oxidation zone 20, salts tend tofill the grooves 80, thereby reducing the flow path past the pressurecontrol needle 68 and causing a slow buildup of pressure within theoxidation zone 20. As the pressure builds within the oxidation zone 20,the pressure control needle 68 is slowly forced downwardly. When thepressure control needle 68 is depressed sufficiently to expose thegrooves 80 to the low pressure conditions existing in an exit port 82,the salts are swept from the grooves 80 into the exit port 82. Once thesalts are swept from the grooves 80, the available flow path past thepressure control needle 68 is increased, thereby reducing the pressurewithin the oxidation zone 20 and causing the pressure control needle 68to slowly rise upwardly, whereupon the grooves 80 again are exposed tothe high pressure conditions existing within the oxidation zone 20.

With reference to FIG. 9, the algorithm that controls the positioning ofthe control valve piston 72, and hence the pressure control needle, isas follows:

Control Piston in Vertical Equilibrium

Σfy↓=Σfy↑

P_(SCWO)=Pressure exerted on needle by SCWOP_(TOP)=Pressure exerted on the top of the pistonP_(BOP)=Pressure exerted on the bottom of the pistonA₁=Vertical area of the needleA₂=Exposed area of the top of the pistonA₃=Area of the bottom of the pistonW=Weight of the piston

P_(SCWO)A₁ + P_(TOP)A₂ + W = P_(BOP)A₃$P_{BOP} = {{P_{SCWO}\frac{A_{1}}{A_{3}}} + {P_{TOP}\frac{A_{2}}{A_{3}}} + {W\frac{1}{A_{3}}}}$$A_{1} = {{\frac{( 1^{''} )^{2}\Pi}{4}\mspace{14mu} A_{2}} = {{\frac{( {3.5^{''2} - 1^{''2}} )\Pi}{4}\mspace{14mu} A_{3}} = \frac{( 3.5^{''2} )\Pi}{4}}}$$P_{BOP} = {{P_{SCWO}\frac{1^{2}}{3.5^{2}}} + {P_{TOP}\frac{( {3.5^{2} - 1^{2}} )}{3.5^{2}}} + {W\frac{4}{3.5^{2}\Pi}}}$$P_{BOP} = {{P_{SCWO}\frac{1}{12.25}} + {P_{TOP}\frac{11.25}{12.25}} + {0.52\mspace{14mu} {psig}}}$

The 0.52 psig due to the weight of the piston is insignificant comparedto the operating pressure of the SCWO, therefore:

$P_{BOP} = {{P_{SCWO}\frac{1}{12.25}} + {P_{TOP}\frac{11.25}{12.25}}}$

In a typical operation, the programmable logic controller code thatresults from applying this algorithm is described as follows:

Rung 100

A=P_(SETPOINT)−P_(SCWO)

Rung 101

If A>200

-   -   A=200

Rung 102

If A<200

-   -   A=2A

Rung 103

If A<−200

-   -   Shutdown Oil Feed

Rung 104

$P_{BOP} = {\frac{P_{SCWO} + A + {Offset}}{12.25} + {P_{TOP}\frac{11.25}{12.25}}}$

Will work for all ranges of pressure control:

During pressurization trying to get 200 psig+P_(SCWO)

While P_(SCWO)>P_(SETPOINT) provides feedback

If P_(SCWO)>P_(SETPOINT)+200 psig−Shutdown oil feed

Thus, back pressure control in the steady state operation of theinvention is self-regulating. The process pressure acts on a small areaon top of the control valve piston 72. The pressure control fluid, onthe other hand, acts on a much larger area determined by the majordiameter of the control valve piston 72. This control ratio allows theapplication of relatively low pressure control fluid (typically nitrogenor air) on the bottom of the control valve piston 72 to regulate themuch higher process pressure on the top side of the control valve piston72. If the oxidation zone 20 pressure increases, the force on top of thecontrol valve piston 72 increases and forces the pressure control needle68 and the control valve piston 72 down, opening the gap between thepressure control needle 68 and the valve seat insert 44, increasing theflow area, and thus tending to decrease the pressure within theoxidation zone 20. Similarly, when the oxidation zone 20 pressuredecreases, the control valve piston 72 and pressure control needle 68are forced upwards, closing the gap and tending to increase the systempressure. If pressure within the oxidation zone 20 increases due to abuildup of solids bridging the flow area, the pressure control needle 68is gradually pushed down, opening the gap and passing the blockage. Thepressure control needle 68 will thereafter self-correct to the steadystate position automatically upon passing any such bridging solids.

The oxidation zone 20 is controlled in terms of temperature and pressureto continuously remain above the critical point for water. In a typicaloperation, the temperature within the reactor 10 is between about 900degrees F. and about 1100 degrees F., and the pressure within thereactor 10 is between about 3300 psig and about 3600 psig.

Reaction product gases and salts are removed from the valve housing 16via the exit port 82. Typically, the reaction product gases are at apressure of about 550 psig. The exhaust gases are typically slightlysuperheated to minimize the adhesion of salt slurry to downstreamprocess piping. The reaction product gases and salts are thereafterrouted through suitable gas/solids separation equipment (not shown),such as cyclone separators, electrostatic precipitators and/or baghouses and filters to remove the entrained salts.

In prior art SCWO reactors, the effluent must typically be diluted up toabout 10:1 to transport the salts from the reactor 10 to a heatexchanger, then to a gas/liquid separator, then separated intorespective effluent streams (gas and liquid) for additional processing.Salts are removed from the liquid effluent in a brine recovery system.Prior art methods of dealing with reaction products are contrasted withthat of the method of the invention which incorporates an integralletdown valve 66 to transport the salts out of the lower area of thereactor 10 as a solid suspension in the exhaust gases.

In a typical operation of the invention, superheated steam carryingsolid salts at around 550 psig and 900° F. is removed from the reactor10 and sent to a cyclone separator. In one embodiment, the combinedsteam/salt flow rate is typically around 420 lb/hr. Solid salts areseparated by centrifugal force and fall to the bottom of the cycloneseparator. Superheated steam exits the top of the cyclone separator. Thesteam is let down to atmospheric pressure through use of a back pressurecontrol valve. The steam is then mixed with ambient air and send throughan activated carbon filter to ensure compliance with applicableemissions standards.

The solid salts and condensate which accumulate at the bottom of thecyclone separator can be handled by allowing the solid salts andcondensate to fall into a pair of high durability valves in series thatoperate as an airlock to allow ejection of salt while minimizing theflow of steam. Initially, both valves are closed. When the top valve isopened, salts from the cyclone separator begin to fill the pipe betweenthe two valves. When the space between the two valves is approximatelyhalf full, the upper valve is closed. Next, the lower valve is opened.When the lower valve opens, the expansion of the superheated steambetween the two valves provides the motive force to move the salt intothe downstream piping where it rejoins the steam and condensate at theexit of the backpressure regulator.

The process stream can then be directed to a moisture separator thatseparates the condensate and brine from the vapor. The vapor istypically directed to an exhaust ventilation stack through a HEPA filterthat incorporates a carbon filter. The brine that collects in themoisture separator is pumped to a suitable holding tank pendingdisposal.

This integral salt-processing design simplifies the SCWO system of theinvention and eliminates problems with salt precipitate fowling thebackpressure regulator.

Having thus described the invention, it should be apparent that numerousstructural modifications and adaptations may be resorted to withoutdeparting from the scope and fair meaning of the instant invention asset forth hereinabove and as described hereinbelow by the claims.

1-11. (canceled)
 12. A reactor useful in the continuous oxidation oforganic material in a supercritical water oxidation process, the reactorcomprising: (a) a reactor body with reactor walls; (b) and a threadedreactor upper plug; and (c) a cylindrical liner attached solely to thethreaded reactor upper plug, such that, when the threaded reactor upperplug is removed from the reactor, the reactor liner is consequently andsimultaneously removed from the reactor as well.
 13. The reactor ofclaim 12 wherein the reactor liner is attached to the threaded reactorupper plug by pins.
 14. The reactor of claim 12 wherein an annulus isdefined between the reactor walls and the reactor liner and whereinmeans are provided for continuously purging the annulus duringoperation.
 15. The reactor of claim 12 further comprising one or moreseal rings to seal the threaded reactor upper plug to the reactor bodyand means for separately cooling the one or more seal ring seals.
 16. Areactor useful in the continuous oxidation of organic material in asupercritical water oxidation process, wherein the reactor comprises aninternal letdown valve.
 17. The reactor of claim 16 wherein the letdownvalve comprises a control valve piston and a pressure control needledisposed at the outlet of a ball cap.
 18. A reactor useful in thecontinuous oxidation of organic material in a supercritical wateroxidation process, the reactor comprising: (a) a reactor body withreactor walls for oxidizing organic material to post-oxidation material;and (b) an internal letdown valve capable of reducing the pressurewithin the reactor of the post-oxidation material.
 19. The reactor ofclaim 18 wherein the letdown valve is capable of reducing the pressurewithin the reactor of the post-oxidation material to less than about 550psig.
 20. The reactor of claim 19 wherein the internal letdown valve iscapable of maintaining condensible material within the post-oxidationmaterial in gaseous form and transporting solid salts within thepost-oxidation material in a gaseous suspension.
 21. The reactor ofclaim 18 wherein the internal letdown valve comprises a control valvepiston and a pressure control needle disposed at the outlet of a ballcap.
 22. The reactor of claim 21 wherein the pressure control needle hasslots for allowing minimum flow when the pressure control needle isfully seated in a ball cap seating surface.